The invention relates to a micro air-wave detection device used more particularly for monitoring, surveilling or alerting a sleeping subject, as soon as an abnormal breathing stoppage occurs.
In the field of breathing surveillance, there already exist a number of methods and devices which unfortunately do not always give satisfactory results for the reasons given below. For persons suffering from illness or frailty, having in particular breathing difficulties or cardiac anomalies, it is necessary to monitor their sleep and possibly set off an alarm and/or oxygen supply. For that purpose, devices used must be accurate and reliable without, however, causing constraint.
The systems used up to now are based on the principle of measuring the blood pressure of the individual, or detecting movement of his rib cage, or else measuring the resistivity of the skin or the oxygen saturation of the blood. In reanimation centers, hospitals and clinics, sophisticated, heavy and cumbersome apparatus are available which require the presence of the patient and which are costly to purchase, maintain and operate. In addition, apparatus for monitoring and surveilling breathing by detection of the movement of the rib cage or the resistivity of the skin prove to be not very reliable because, in particular, the parameter for reference with respect to the movement to be measured is mobile, calibration is very difficult and finally they lack sensitivity.
Portable apparatus are preferred, for example, for measuring the arterial or venous blood pressure, or for determining the oxygen saturation of the blood. Such apparatus, however, although functioning correctly, have the enormous drawback of not being able to be used without waking the subject and without external intervention. In addition, the use of such apparatus requires that a lack of oxygen already occur in order to cause indisposition, leading to acceleration of the heart beat and a rise in blood pressure.
Finally, systems exist based on the detection of breathing itself, in which a detector is connected by a conduit to a mask or to a probe fitted to the nose of the patient, wherein the detector picks up the pressure variations in the breathing. In particular, U.S. Pat. No. 3,817,238 discloses a breathing detector for animals in which the detection member comprises a vertical transparent tube connected by a conduit to the snout of the animal. In the tube, a light ball moves at the breathing rate and its movement is detected by a photoelectric cell subjected to illumination by a light source. This system has all or nothing operation and is quite lacking in sensitivity, if only because the air pressure variation in the tube must be greater than the force of gravity which is exerted on the ball in the vertical tube.